I don't see any SCUII regarding document type for doc splitting.
Is it an automatic assignment like G/L Accounts ?
The only configuration for document splitting you have. selection of document splitting and zero balance clearing. Document splitting is mandatory.
Rest of the configurations are not available.
G/Ls are assigned automatically. That is the reason in s/4hana cloud you have the option to create a new G/L by copying it. You do not have the option to create button.
That is why it is recommended that you shall always select the right/similar g/l for refencing (copying).